Disengaging and/or releasing a clutch arranged in a power train may be achieved by way of a clutch actuator arranged on a clutch bell, where the clutch actuator works electrically, pneumatically or hydraulically and serves as the axial displacement of a clutch release bearing. A pneumatically operated clutch plate of this type is known from DE 100 05 086 A1 by the Applicant.
In hydraulic or pneumatic clutch actuator, the clutch actuator essentially comprises a cylinder housing, a piston with a seal, a preload spring and, if necessary, a venting screw. The preload spring provides that a minor shift force is always present on the clutch release bearing when the clutch actuator is vented and/or depressurized. This way, a breakdown of the lubricating oil film in the shift bearing can be prevented, the life of the clutch release is increased and disturbing noises are avoided.
The use of a preload spring and/or pretensioning spring of this type has the disadvantage that their spring force varies depending on the clutch release path. Thus, the pretensioning force changes subject to the wear of the clutch linings which, considering the entire life of the clutch, causes inconsistent and undesired system behavior.
A further disadvantage of using a pretensioning spring in clutch actuator is that a frequently desired and adjusted stronger pretensioning force often causes micromovements in the clutch actuator itself when the clutch is engaged. This is because in the coupled state, when the clutch actuator is depressurized, vibrations of the motor are transmitted to the clutch release cylinders with a higher pretensioning force. This causes very small movements in the clutch actuator which, in turn, cause a premature wear of the clutch actuator.
Nevertheless, micromovements in the clutch release mechanism may be quite practical, namely to minimize the effects of friction of the clutch release mechanism on the clutch control. However, such micromovements are not necessary and are rather harmful in the coupled state.
Against this background, it is the object of the present invention to improve a clutch actuator of the above mentioned type, such that it overcomes the described disadvantages and also preferably consists of as few components as possible.